Can someone confirm how the oil pressure gauge is connected to the sender? I *think* one of the sender wires goes to +12V, and it grounds through the engine block, and there is a pressure/voltage output. I need to know which is which... The two wires I think they are, are- orange/black stripe, brown/white stripe. TIA for your quick responses, I need to get this fixed ASAP.

[This message has been edited by ryan.hess (edited 07-30-2009).]

Hey Ryan,

There are three wires...

Orn/blk is 12V from F.Pump Fuse to the oil pressure SWITCH and which also branches to the fuel pump relay pin D

Tan/wht is the other half of the orn/blk circuit once the oil pressure SWITCH closes, and routes 12V to the fuel pump. The tan/wht circuit also has branches that lead to the ALDL connector pin G and the fuel pump relay pin B

Tan wire is the oil pressure SENDER wire. The sender provides a variable resistance ground through itself to the engine block for the oil pressure gauge (instrument panel connector C3 pin 6).

(edited for clarity)

[This message has been edited by Bloozberry (edited 07-30-2009).]

hmmmm.... so the only one needed for the gauge is the plain tan wire going through C203 pin E?

The only wire going to the engine... yes. There are two other wires feeding the gauge though. One is pnk/blk from the Gages Fuse to instrument panel connector C2 pin 9 on the four cylinder engines, and to pin A of the aux gauge cluster in the V6's. The third wire is a blk wire from C3 pin 11 (for four cylinders) or pin H of the aux Gauge cluster in the V6's, that goes straight to ground G201 on the vertical upright of the dash support beam, behind the radio.

I should add that the Tan wire goes to B of the aux cluster for the V6's.

(edited for V6 info)

[This message has been edited by Bloozberry (edited 07-30-2009).]

Thanks! Sent you a plus. I lost my fiero wiring diagram which had this missing piece in it.

Bloozberry, I've been thinking about trying to fix my oil pressure gauge which has never worked since I have owned the car. My oil pressure gage pegs right when the motor is turned on. I see 3 wires coming off the oil pressure sender (I think) One is a pale orange with a black stripe, another is a light grayish purple with a white stripe, and the third doesn't appear to have anything on it. It doesn't look tan to me but is a grayish purple. I have made a wire with a sharpened nail on each end. If I short the plain wire out, without unhooking anything, with the motor running, what might happen to the gage needle and what would it mean? Don

see cave... sender upgrade is electrical/other system

Auto Store... most don't carry the old sender in inventory. 88+ is easy.
Web store, rockauto etc... Not a problem.

Old sender is old design and you can get a new part but new part is likely to leak 2 to 5 years.
I did an upgrade to my car with one hand....

2 wire is backup for fuel pump relay... Short both and fuel pump stay on.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

[This message has been edited by theogre (edited 06-24-2010).]

quote Originally posted by centervilledon: Bloozberry, I've been thinking about trying to fix my oil pressure gauge which has never worked since I have owned the car. My oil pressure gage pegs right when the motor is turned on. I see 3 wires coming off the (I think) One is a pale orange with a black stripe, another is a light grayish purple with a white stripe, and the third doesn't appear to have anything on it. It doesn't look tan to me but is a grayish purple. I have made a wire with a sharpened nail on each end. If I short the plain wire out, without unhooking anything, with the motor running, what might happen to the gage needle and what would it mean? Don

I had read that a small amout of water can get into some sort of weep hole or air hole at the top of the oil pressure sender (its purpose is not known by me,a fix was to use a small curved rubber vacume tube,pointed down).But I may have my parts location mixed up,asumeing its near the top passenger side of the motor....someone correct me if I goofed on my parts location.

Those old can type Fiero pressure sensors are very unreliable as they are not hermetically sealed. The sensors for the 88 can be wired in and will perform the same gauge function but beware. That sensor configuration is made in two different resistance values as it was used on many GM cars. The more widely used version will peg your gauge as it is (from memory) an 120 ohm unit where the Fiero sensor is an 80 ohm unit. I had trouble getting the 88 sensor ( as the 120 ohm units were being put in the boxes for the 88 application,) so I just used the later 120 ohm sensor and placed a 200 ohm resistor in parallel to ground on the sensing lead to limit the max resistance and to keep the gauge needle from pegging. It works well.

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quote Originally posted by Dennis LaGrua: Those old can type Fiero pressure sensors are very unreliable as they are not hermetically sealed. The sensors for the 88 can be wired in and will perform the same gauge function but beware. That sensor configuration is made in two different resistance values as it was used on many GM cars. The more widely used version will peg your gauge as it is (from memory) an 120 ohm unit where the Fiero sensor is an 80 ohm unit. I had trouble getting the 88 sensor ( as the 120 ohm units were being put in the boxes for the 88 application,) so I just used the later 120 ohm sensor and placed a 200 ohm resistor in parallel to ground on the sensing lead to limit the max resistance and to keep the gauge needle from pegging. It works well.

I wasn't aware of that and it explains why my gauge is pegging with the new late style sensor. Did you calculate the appropriate resistor value for parallel use with the following equation to arrive at 200 ohms:

1/80 ohm required = 1/R1 sensor + 1/R2 additional resistor needed